392 Scientific Geology. 



This ledge has been described by Prof. Dewey, under the name of 

 mica slate : but I have already given the reasons that have led me to 

 differ from him on this point. 



The suggestions that have been made in treating of mica slate, in 

 regard to the causes of such flexures in rocks, are equally applicable 

 to the rock under consideration ; and therefore I shall add no more 

 in this place on the subject. 



It will appear from the following notes, relative to the dip and di- 

 rection of the strata of gneiss in Massachusetts, that this rock con- 

 forms to at least three systems of stratification. The Hoosac moun- 

 tain range, and the western part of the Worcester county range 

 exhibit one system : the branch of this latter range, which extends 

 into Middlesex county, belongs to a second without much doubt : that 

 portion of it in the southeast part of Worcester county and in Rhode 

 Island seems to belong to a third, and perhaps the New Bedford 

 gneiss to a fourth. But more of this hereafter. 



Hoosac Mountain Range. 



Direction. Dip. 



Cheshire, east part, N. and S. 20 to 30 E. 



Windsor to north part of Peru, N. and S. East. 



Chester to Becket, N. and S. 80 to 90 E. 



Colebrook, Ct. to West Granville. N. and S. nearly 90 E. 



Whitingham, Vt. N. and S. 30' W. 



Wilmington, Vt. - N. 30 E. 30 to 70 W. 



do. to Somerset, N. and S. West, large. 



Buckland, - N. and S. 10 to 20 E., and 



10 to 20 W. 

 the latter rather predominating. 



Range West of Worcester Valley. 



Direction. Dip. 



Brimfield, - N. and S. 45 W. 



do. to Sturbridge, N. and S. 20 to 80 W. 



.Sturbridge to Charlton, - - N. and S. 45 W. 

 Monson to Sturbridge through 



Wales and Holland, - - N. and S. 45 to 70 W. 



Plumbago Mine, Sturbridge, N. 30 E. 60 to 70 N.W. 

 Sturbridge through Southbridge 



to Dudley, the dip gradually 



decreasing, - N. and S. 60 to 25 W, 



